I have this same problem with rum0 on 5.0_RC2.
ioctl[SIOCS80211, op 21, len 42]: Invalid argument
Is this a problem with rum(4)?

I had a brief look into it and came to the conclusion the rum driver
is indeed broken. It is unable to be associated with an wpa2 access
point. I never tracked down which change was the problem, in the end i
replaced the rum device with a supported wpi device.